1. Field of the Invention
The invention relates in general to a method for die attaching, and more particularly to a method for die attaching by using a pick-and-place machine to complete the stack of the die-attach preform and the die.
2. Description of the Related Art
In an ordinary single-die or multiple-die package manufacturing process, the wire bonding type die must be first of all adhered to a die carrier via a die attaching material. The conventional die carrier can be a circuit substrate, a leadframe or another stacked dies. Then, the wire bonding manufacturing process is performed. Normally, the conventional die attaching material which adheres the die and the die carrier can be a thermosetting material or a thermoplastic material. During the conventional die-attaching process, a die carrier is moved to a dispensing machine or a tape attaching machine to proceed with the adhesive-dispensing or tape-attaching step, so that die attaching material such as liquid adhesive or adhering tape can be formed on the die carrier. Next, the die carrier with the liquid adhesive or adhering tape formed thereon is transported to a pick-and-place machine via a track, and a pick-and-place robot of the pick-and-place machine is used to pick and place the die on the die carrier one by one. The die carrier is adhered to the die via the die attaching material. The liquid adhesive or adhering tape used in the conventional method for die attaching requires appropriate adhesive coating equipment of the die to form the die attaching material on the die carrier in advance, and then the die carrier is transported to the picking and placing machine via a track transport equipment, so that the die is picked and placed on the die carrier one by one. The conventional method requires more equipment and takes longer time for bonding the die.
Conventional wafer-level method for die attaching to increase the efficiency is disclosed in FIGS. 1A˜1F. Referring to FIG. 1A, firstly, a wafer 110 is provided. The wafer 110 comprises several dies 111, each having an active surface 112 and an opposite rear surface 113. Several bonding pads 114 are formed on the active surfaces 112 of the dies 111. Referring to FIG. 1B, a stencil 10 is disposed on the rear surfaces 113 of the dies 111 by using the stencil printing technology. The stencil 10 has several openings 11 corresponding to the rear surfaces 113. Then, a die attaching material 120 is formed on the stencil 10 and is scraped using a scraper 20. The die attaching material 120 is filled in the openings 11 of the stencil 10, and is formed on the rear surfaces 113 of the dies 111 via printing. Referring to FIG. 1C, a heating step is performed to partly solidify the die attaching material 120 of the rear surfaces 113 to become a B-stage adhering layer 121 adhered on the wafer 110. Referring to FIG. 1D, a cutting tape 30 is pasted onto the active surface 112 of the dies 111, the wafer 110 is sawn, and then the dies 111 having the B-stage adhering layer 121 is formed through singulation. In the step of sawing the wafer 110, the dies 111 are cleaned by using de-ionized water (DIW) at the same time. Then, the dies 111 is turned over to be pasted onto another tape (not shown in the diagram), so that the active surfaces 112 of the dies 111 is exposed upward to be picked and moved by a pick-and-place machine one by one. Referring to FIG. 1E, a die carrier 130 is disposed on a supporting plate 41, and a pick-and-place robot 42 with a suction head is used to suck and place one of the dies 111 having a B-stage adhering layer 121 on the die carrier 130, so that the B-stage adhering layer 121 contacts the die carrier 130. Referring to FIG. 1F, the supporting plate 41 is heated, so that the B-stage adhering layer 121 generates adherence to be adhered to the die carrier 130. According to a similar method for die attaching, disclosed in U.S. Pat. No. 6,703,075, a liquid adhesive is printed on a surface of a wafer first. After pre-heating, the liquid adhesive is converted into partly polymerized B-stage state. Then, the wafer is sawn and separated to form several dies having adhesive.
However, in the above wafer-level method for die attaching, when the dies 111 having B-stage adhering layers 121 are formed, de-ionized water is used to clean the dies 111, affecting the characteristics of the adhering layers 121. Consequently, the adhering layers 121 will change due to absorption of water, causing the adhesive between the dies 111 and the die carrier 130 to be deteriorated.